1. Field of Invention
This invention relates to pedometers, specifically to an improved method for detecting strides for a pedometer.
2. Prior Art
In many recreational endeavors and occupations a need exists for persons to be able to measure distances by walking from one point to another. For example, exercise walkers often record their daily mileage in a diary. Golfers and hunters often want to know the distance between two landmarks. Real estate agents often need to know the length and width of a building or field.
Prior art pedometers do not support these distance-measuring needs with an acceptable level of accuracy. Consumer Reports magazine (pp. 30-31, October, 2004) recently tested a number of pedometers and found that most were inaccurate by 5 to 10 percent, and some were inaccurate by 20 percent or more. “The worst were so inaccurate that if you walked five miles, they might say you'd covered three to seven.” This is not satisfactory for an exerciser wanting to know the number of miles traveled to within a fraction of a mile, let alone a golfer or real estate agent wanting to know a distance to within a few yards or feet.
Pedometers calculate distance by multiplying the length of the user's step (or stride) times the number of steps (or strides) the user takes. A stride is one step by each leg, or two steps total. Any given pedometer is designed to count either steps or strides.
The accuracy of the distance measured by a pedometer is a function of: (1) the accuracy of the step/stride length entered into the pedometer for a given person, and (2) the accuracy with which that pedometer counts steps/strides. Researchers of human gait have determined that a person's step/stride length is the same from one step/stride to the next and from one day to the next when that person walks at their self-selected speed (Inman et al, Human Walking, p. 22, 1981). Self-selected walking speed, also called free- or natural-walking speed, is the speed that a walker unconsciously uses when walking without any particular purpose. Accurately determining a person's step/stride length for their self-selected walking speed is a straightforward exercise of counting the number of steps/strides taken for a measured distance and then dividing the distance by the number of steps/strides. So the distance-measuring accuracy of any given electronic pedometer is determined by the accuracy of the step/stride detection mechanism for that pedometer, assuming an accurate step/stride length is used.
The prior art uses a number of different mechanisms to detect steps and strides. U.S. Pat. No. 4,053,755 to Sherrill (1977) is an example of a mechanism for sensing the up-and-down motion of the torso. It uses an electrically conductive leaf spring with a small weight on its free end for momentary engagement with a mating electrically conductive contact. This switch is normally open, and each step taken by the user causes the weight to be jarred downward to bring the contacts together and close the switch. U.S. Pat. No. 4,144,568 to Hiller et al (1979) improves this by replacing the ordinary on/off switch with a magnetic reed switch. U.S. Pat. No. 5,117,444 to Sutton et al (1992) teaches “Ordinary switches, however, are prone to intermittent operation” and “Reed switch pedometers are much more reliable and give fewer false readings than other prior art devices.”
Other mechanisms are used to detect steps and strides. U.S. Pat. No. 4,175,446 to Crowninshield (1979) uses a strain gauge to sense foot strike with the ground and detect strides. U.S. Pat. No. 4,371,945 to Karr et al (1983) uses an ultrasonic generator and detector to sense (lower) leg swing and detect steps. U.S. Pat. No. 4,855,942 to Bianco (1989) uses a mercury switch to sense arm swing and detect strides. U.S. Pat. No. 5,485,402 to Smith et al (1996) uses an accelerometer to sense lower-leg swing and detect strides. The prior art teaches away from using an inexpensive, ordinary tilt switch as a sensor for a pedometer.
All of the prior art has the step- or stride-detection mechanism attached to a body part or an item of clothing of the user. Some of the prior art asserts that body motions other than that specifically described can detect steps with a certain detection mechanism. For instance, U.S. Pat. No. 4,223,211 to Allsen et al (1980) states, “The said motions accompanying foot motions of the subject may be motions of any part of the body.” This patent, like others making similar statements, does not describe how the other body motions actually detect steps taken. No prior art detects strides by sensing the motion of a user's upper leg with a stride-detection mechanism in the front pants pocket of the user that is unattached to either the pocket or the user.
Prior art pedometers assume that each pulse in the electrical signal produced by the sensor corresponds to a single step or stride. U.S. Pat. No. 4,387,437 to Lowery et al (1983) recognizes the problem of switch bounce giving false step indications and incorporates a debounce circuit to attempt to eliminate false indications. U.S. Pat. No. 5,684,284 to Lee et al (1997) uses an electronic filter to prevent “extraneous mechanical vibration of the unit from registering as a player's stride.” No prior art uses the timing of human gait to interpret step/stride-sensor signals and differentiate step/stride indications from switch bounce and non-step/stride motion artifacts.